The organism that can reproduce both sexually and asexually is the protist. Many protists have the ability to reproduce through both methods depending on their environmental conditions.
Starfish, while primarily known for asexual reproduction through regeneration, can also reproduce sexually. However, protists are more widely recognized for having both reproductive strategies.
If you're looking for the best answer based on a broad perspective of organisms that fit the criteria, protist would be the most appropriate choice.